1. Field of the Invention
The invention relates to an interferometric system that involves differential-phase decoding and that is suitable for applications requiring high speed and high detection sensitivity.
2. Description of the Related Art
U.S. Pat. No. 7,006,562B2 discloses a phase demodulator for measuring a phase difference between a phase-modulated test signal and a phase-modulated reference signal having fixed carrier frequencies. The phase demodulator includes an amplitude control device for adjusting amplitudes of the test and reference signals. A differential amplifier receives amplitude-adjusted test and reference signals from the amplitude control device, obtains an intensity difference between the amplitude-adjusted test and reference signals, and amplifies the intensity difference to generate an amplitude-modulated output. An amplitude demodulator demodulates the amplitude-modulated output to obtain an output that is related to the phase difference.
The aforementioned patent further discloses a phase difference detector for use with a polarized optical interferometer that generates two mutually orthogonal polarized optical signals, at least one of which is incident upon a test object. The optical signals have equal intensities and carrier frequencies and are processed to obtain two electrical signals that are a function of a frequency, a time, and a phase difference between the two mutually orthogonal polarized optical signals. The phase difference detector comprises a differential amplifier that receives the electrical signals, that obtains an intensity difference therebetween, and that amplifies the intensity difference to generate an amplitude-modulated output that is a function of a phase difference between the electrical signals. The phase difference detector further comprises a signal processing device including an amplitude demodulator for demodulating the amplitude-modulated output to obtain an output that is related to the phase difference.
In the aforementioned patent, the output that is related to the phase difference can be obtained solely from the amplitude-modulated output due to the adjustment of the amplitudes of the test and reference signals performed by the amplitude control device. However, the need for amplitude-adjustment processing by the amplitude control device limits potential applications of the phase demodulator and the phase difference detector disclosed in the aforementioned U.S. patent.